1. Field of the Invention
This invention relates to the field of coating mastic and caulking compositions and to composite articles manufactured with such compositions. In particular it relates to architectural coating mastic and caulking compositions and to roof coating mastics.
2. Introduction
Architectural mastic and caulking compositions are used in a wide variety of applications to seal and protect architectural material substrates and to seal and protect joints and other openings in architectural materials. They are used in both interior and exterior applications, and in both cases are exposed to conditions such as moisture, sunlight, temperature variations, etc. that require such compositions to have a balance of properties enabling them to perform their intended functions for extended periods of time. Typically, mastics and caulks must be fluid or semi-fluid compositions which are stable, high solids content formulations usually having a total solids content of about 60 weight percent or more. They should have permanent low temperature flexibility when cured, particularly in the case of mastic compositions intended for exterior application. Both the mastics and caulks should have sufficient wetting ability to readily wet, cover and adhere to even the most hydrophobic architectural substrates such as polyurethane, ethylene-propylene-diene interpolymer materials, and the like. Very low residual surface tack is generally required in cured mastics and caulks, and they should quickly become non-tacky shortly after application to prevent adherence of dust, dirt or other materials.
High tensile strength is also required, particularly for mastics intended to protect vulnerable exterior materials such as foamed polyurethane insulation. High tensile strength provides improved puncture and tear resistance in the cured coating or caulk and overall protection of the substrates or architectural joint at both high and low temperatures since tensile strength ensures against cracking or separation as a result of thermal expansion (as well as relative motion from other causes). While compositions intended for exterior use can be clear, they are often pigmented, particularly in the case of protective roof coatings with opaque reflective pigments such as titanium oxide and zinc oxide. They also preferably are good reflectors and heat radiators to minimize temperature extremes.
High adhesion to all varieties of architectural construction materials is also desirable and is especially important in some roofing applications which employ relatively hydrophobic roofing materials such as foamed polyurethane insulation and ethylene-propylene-diene interpolymer coatings. High adhesion to other structural materials such as wood, concrete, metals, glass and other materials is also desirable to enable flexibility of use. Exterior coatings also should be resistant to weather and, in particular, should have good "wet adhesion" and resistance to oxidation, ultraviolet radiation and air pollutants found in industrial and urban areas.
Water impermeability and resistance (low absorption) are essentially universal requirements of both exterior and interior mastics and caulks and are particularly important for use in areas exposed to water such as kitchens and bathrooms. Physical stability of the cured composition is also a relatively high priority in essentially all applications, particularly for exterior mastics and caulks which must be resistant to creep at high temperatures and excessive shrinking at cold temperatures, the latter of which can promote cracking and separation from substrates.
In addition to all the foregoing requirements, it is also desirable that caulks and mastics be relatively easy to manufacture in the absence of expensive and/or toxic materials. For instance, water-base mastics and caulks are much preferred over solvent compositions due to the added expense, pollution, toxicity, and fire hazards associated with the use of solvents. Furthermore, previous investigators have found that many of the above-noted desirable physical and chemical properties can be achieved by the use of compositions which contain potentially toxic monomers, catalysts or cross-linking agents which improve the strength of the mastic or caulk binder (usually a synthetic polymer). Thus, N-methylolamide-functional monomers and other crosslinking monomers and agents are known to improve polymer performance in mastics and caulks in several respects. However, many of the useful cross-linking monomers and agents release toxic materials upon curing and can result in the presence of toxic residues in the finished article. For instance, N-methylolamide-containing polymers release formaldehyde when cured, and they can result in formaldehyde residues in the finished mastic or caulk. Formaldehyde release and residues are often undesirable since formaldehyde is coming under ever increasing scrutiny in both the work place and home, and the State and Federal Occupational Health and Safety Administrations (OSHA) have set stringent formaldehyde exposure limits for industrial workers.
The polymer binders, particularly those employed in water-base mastics and caulks, should have rheological properties sufficient to provide adequate stability to the heavily solids-loaded compositions and suitable cohesive and wetting properties to enable ease of application. Polymer latex viscosity and wetting ability are both influenced significantly by binder polymer composition and can limit latex utility by restricting filler loading level, substrate wetting ability, and the ease of mastic or caulk application.
Thus, the physical and chemical properties required in mastic and caulking compositions, in articles coated or sealed with such compositions, and in the polymer solutions or dispersions used in the manufacture of mastics and caulks, place various, sometimes conflicting, demands on polymer binder compositions and on the polymer carrier (i.e., solvent or water). Hence, it is desirable to obtain a polymer system, preferably a water-base polymer emulsion, which possesses a balance of properties suitable for the manufacture of architectural mastics and caulking compositions and of articles coated or sealed with such compositions. It is further desirable to obtain such a polymer system comprising a zinc-containing pigment, such as zinc oxide, and having good wet adhesion to a variety of substrates, including relatively non-adherent substrates, even after aging.